The present invention relates to a roller for transferring labels of the aspirating type, comprising at least a pair of pads projecting relative to a lateral surface of the roller, and a related method.
It is well known that rollers for transferring labels are used in labelling machines, in which a film of labels is unwound from a reel and is routed towards a cutting device, which cuts it to form the labels to be glued on a container.
The label thus formed always has substantially rectangular or square contour and it has two vertical and parallel edges.
The transfer roller, rotating at a predetermined speed about a normally vertical axis, picks up the label and transfers it in correspondence with gluing means and subsequently onto the container to be labelled.
Specifically, the gluing means lay a first strip of glue along a rear face of a first vertical edge of the label and subsequently lay a second strip of glue on a second vertical edge, which will be superposed and glued to the first edge. In accordance with a known variant, there are gluing means which are capable of laying the glue in points, instead of along one or more strips. The containers to be labelled are brought into contact with the roller for transferring the label by means of a linear or rotary transport, commonly called carrousel.
According to a first prior art technique, the transfer roller is provided with a group of pincers so shaped as to keep the label adherent to the lateral surface of the roller.
Such a transfer roller has the important drawback of being extremely complex to build, because it requires a system of cams, suitably dimensioned to open and close the pincers during the rotation of the roller. In the second place, a labelling machine provided with such a roller is not suitable for bottling plants with high production rates, because of the reduced velocities of rotation of the roller.
According to a second prior art technique, within a roller lacking pincers, a plurality of cavities communicating with a lateral surface of the roller by means of a series of through holes is obtained. Subsequently, through said cavities, a suction of variable and controlled intensity is taken in such a way that the labels can adhere to the lateral surface of the roller during their transfer from the cutting device to the container.
The lateral surface of the rollers is also provided with a plurality of recesses for collecting the residues of glue which tend to be deposited on the suction holes, m order not to compromise their operation. Said residues are caused by the contact between the label and the gluing means and their size in influenced by the velocity of rotation of the roller.
An aspirating transfer roller can be employed for labelling both containers made of plastic material, typically PET, and glass containers.
However, in this latter case, use of a roller of the aspirating type has the important drawback of causing the rupture of the containers, due to the contact, during the labelling operation, between the lateral surface of the roller and the containers.
The lateral surface of the roller is usually made of steel or otherwise of another material with high rigidity, suitable to allow an adequate relative sliding between the label and the roller, when transferring the label on the container.
Glass containers, which usually have very poor dimensional tolerances, considerably complicate the operations of setting up and correctly calibrating the labelling machine, and thus often come violently in contact with the transfer roller.
Consequently, since glass is a rigid, but extremely fragile material, the containers are unavoidably broken, with the inevitable escape of liquid and downtime of the machine for cleaning and maintenance, which leads to considerable productivity losses for the plant.
In the sector of PET containers, this problem is not encountered, since, although there is a contact between the containers and the lateral surface of the roller, the containers themselves absorb, becoming deformed, the forces the develop in the point of contact.